This isn't a major bug because the only real issue is the numbers being displayed improperly on the character sheet, but documentation is important and this bit of information could be used for anyone else perplexed by the issue on the character sheet!
My character Annafreya Whiteraven has taken the self-taught feat and I think it might be responsible for the AB being displayed in correctly on the character sheet when potions/spells of aid are used.
On the character sheet, the bonus from aid does not appear. Looking at the combat log, however, it appears that the correct AB is indeed used.
I don't think there's an actual fix for this. NWN is just like that.
The bonus is there. It just isn't shown.
That's what they said Thomas. <_<
I know, so it isn't a bug report. Nothing is wrong.